1. Field of the Invention
This invention relates to a monitoring device for the desired application of glue on gluing objects with a glue applicator nozzle.
2. Description of the Prior Art
Gluing processes in sack machines and collators employ the gluing operation with applicator nozzles. The gluing is monitored by detecting the appropriate application of glue on the gluing objects with the applicator nozzle. A monitoring method for gluing which has been available is the capacitance method, in which the gluing object to which glue is applied is inserted between two electrodes to monitor the performance of the gluing operation by measuring the difference in the capacitance between the electrodes as it is effected by the glue applied. An optical method has also been in use which detects the reflected light from colored glue. In the Japanese Patent Application Provisional Publication No. 60-99641 another method is disclosed which evaluates the quantity of glue applied by detecting the attenuation rate at the receiving electrode during transmission of a high-frequency wave between the transmitting and receiving electrodes with gluing object inserted between the electrodes.
In this capacitance method two electrodes are placed facing each other with the gluing object between. Hence both of the electrodes face the glue on the gluing object. In this arrangement the glue coats the electrode surface, causing vast variation in the measured value of capacitance, making it difficult to obtain an exact measurement. The moisture also would yield variation in the measured values, resulting in difficulty in obtaining stable monitoring. On the other hand, the optical method would require the use of colored glues, while in the method of JPAPP No. 60-99641, besides the necessity of two-electrodes, spacing between the electrodes is reduced to raise the monitoring sensitivity because the gluing object moves between the electrodes.